1. Field of the Invention
The present invention relates generally to the field of heavy machinery, and more specifically, to a boom lockout device for a hydraulic front shovel.
2. Description of the Related Art
A hydraulic front shovel, which is a type of excavator, is comprised of a series of hydraulically operated cylinders that control the functionality of the shovel boom, shovel stick and shovel bucket. As part of the routine maintenance and servicing of a hydraulic shovel, some or all of these hydraulic cylinders need to be removed periodically for repair or replacement. During such time, the shovel bucket is positioned on the ground, and the boom and stick are arranged in a peaked position (see FIG. 1) so that their respective cylinders are only partially retracted.
With the stick cylinders removed, the bracing ability of the stick against the bucket is compromised. Depending on the rested position of the bucket, ground conditions under the bucket, and the integrity of the hydraulic system and its operating components (valves, hoses, connections, etc.), the weight of the boom may cause the stick to move forward, thereby allowing the boom to drop until the front of the boom wedges against the rear of the stick or the boom cylinder fully retracts, which stops the downward motion of the boom. This creates an unsafe and dangerous situation if there are people in the immediate area adjacent to and below the boom. To alleviate this situation, the inventors of the present invention have designed a mechanical stop that attaches around the rod end of the boom cylinders to prevent them from fully retracting under the weight of the boom. When the present invention is in place, it forms a long, solid brace with the barrel of the boom cylinder and prohibits the rod from retracting back into the barrel.
The prior art includes a number of similar safety and/or anti-theft devices, none of which possesses the structural features and advantages of the present invention. For example, U.S. Pat. No. 3,135,555 (Caskey, 1964) discloses a safety guard for the ram of a hydraulic hoist. The safety guard is comprised of two hingedly connected tubular halves. U.S. Pat. No. 3,662,653 (Carlson et al., 1972) provides a safety lock for a linear fluid pressure actuator for use in connection with a hydraulic ram having a cylinder body, a piston rod, a clevis and a connecting pin extending between the legs of the clevis. The safety lock prevents retraction of the piston rod and is comprised of a rigid, elongated spacer of generally U-shaped cross-section, the spacer having a pair of arms with apertures for receiving a portion of the connecting pin, and the apertures being sized to permit limited movement of the spacer relative to the clevis.
U.S. Pat. No. 4,122,758 (Bieringer et al., 1978) discloses a service support for blocking the lift arm of a bucket in an extended position during servicing and repair of the lift arm structure. The service support is U-shaped, and pads are provided an the end of the service support to contact the mounting bracket for better distribution of loads. Attachment members mounted on the service support engage with a plate assembly to bridge the open space between the sides of the service support. U.S. Pat. No. 4,373,851 (Confoey, 1983) provides a locking device to prevent theft of a bulldozer or backhoe. The locking device is comprised of an elongated sleeve that fits over a piston rod in its extended position, the sleeve having two halves in the shape of half circular portions of an annular flange. The locking device further comprises outwardly extending arms that are arranged to cover the pivoted portions of the machine.
U.S. Pat. No. 4,413,944 (Coe, 1983) discloses a telescopic locking strut for a tractor front loader. The locking strut is comprised of mutually slideable members and is housed partially within one of the two channel structures of the front loader support frame. The strut is pivotable between a retracted inoperable position and an extended operative position in which it locks the boom on the channel structure in a raised position. U.S. Pat. No. 5,983,684 (Boisvert, 1999) provides an anti-theft device for locking a fluidic piston-cylinder actuator in an extended piston position. The device is comprised of an elongate strut wall member having an arcuate wall portion with a pair of side wall portions space apart so as to define an elongate channel extending between the first and second ends of the strut wall member. This channel receives the extended piston portion of the actuator.
U.S. Pat. No. 6,520,067 (Hunt et al., 2003) discloses a hydraulic piston locking device with a split sleeve configuration and opposed longitudinally extending edges that are locked to one another with a locking means, which is partially enclosed within a lock protecting housing. U.S. Pat. No. 6,698,114 (Bares et al., 2004) provides a hit arm assembly with a support strut that is stored in a front tubular cross member of the lift arm assembly. The front cross member also supports an upright strut that projects upwardly beyond the bucket top and acts as a back stop for material in the bucket.
U.S. Pat. No. 6,874,338 (Hunt et al., 2005) discloses a hydraulic piston locking device having a hollow sleeve configuration formed of hingedly connected first and second sleeve parts. A first lock secures the first and second sleeve members to one another along a longitudinally extending parting line, and a second lock is opposed to the first lock and prevents hinged movement of the first and second sleeve parts.